Coffee Banana Muffin

I still have have some overripe bananas and some butter. Instead of throwing them away, I decided I could make Banana muffins. I have made banana cake before and this was my first time using this recipe with I adapted from somewhere, don't remember where, with some modifications.
Original recipe called for mocha powder which I didn't have and I substituted it with 3 in 1 instant coffee instead .
The result muffin texture was not as moist as I expected but still was a success. The picture taken was about 1 hr after baked from the oven. The muffins surface was a bit more moist after it really cool down.

Method
Line 6 small ceramic small bowls with greased greaseproof paper and preheat oven to 200°C. Mix coffee mocha coffee powder, cocoa powder, milk and water into a paste. Sift flour and baking powder together.

Beat butter and sugar until creamy then add eggs one at a time. Add mashed bananas and beat in combined coffee and cocoa paste. Mix until well blended.

Stir in sifted flour and mix well. Add chopped walnuts.

Spoon mixture into prepared bowls until three-quarters full. Top with a slice of banana and half a walnut. Bake for 25-30 minutes or until muffins are well risen. Leave in the bowls for 5-6 minutes, then remove the muffins onto a wire rack to cool.